1. Field of the Invention
The present invention relates to a magnetic recording element used in a hard disk device, and especially to a temperature assisted magnetic recording element (or thermally-assisted type magnetic recording element).
2. Description of the Related Art
In recent years, based on demand for high recording density, improvement in the performance of a thin film magnetic head and a magnetic recording medium has been required in magnetic recording devices such as a hard disk device. A composite-type thin film magnetic head has widely been used for the thin film magnetic head. The composite-type thin film magnetic head includes a reproducing head having a magneto resistive (MR) element for reading and a recording head having an induction-type magnetic conversion element (a magnetic recording element) for writing, with both heads being laminated on a substrate. In the hard disk drive, the thin film magnetic head is disposed on a slider that flies slightly above a surface of the magnetic recording medium.
The magnetic recording medium is a discontinuous medium on which magnetic microparticles gather. Each of the microparticles has a single magnetic domain structure. In the magnetic recording medium, one recording bit is structured with a number of magnetic microparticles. In order to increase the recording density, asperity of a boundary between adjacent recording bits needs to be small. For this, the size of the magnetic microparticles needs to be decreased. However, when the size of the magnetic microparticles is decreased, the volume of the microparticles decreases. Accordingly, thermal stability of magnetization of the magnetic microparticles also decreases. In order to solve this problem, increasing anisotropic energy of the magnetic microparticles is effective. However, when the anisotropic energy of the magnetic microparticles is increased, the coercive force of the magnetic recording medium is also increased. As a result, it becomes difficult to record information by a conventional magnetic head. Conventional magnetic recording has such a trilemma, and this is a large obstacle to achieving an increase in the recording density.
To solve this problem, one method known as thermally-assisted magnetic recording (temperature assisted magnetic recording) is proposed. In this method, a magnetic recording medium having a large coercive force is used. The magnetic field and heat are simultaneously added to a part of the magnetic recording medium where information is recorded. With this method, the temperature of the part where the information is recorded is increased. Therefore, the coercive force decreases, and the information is able to be recorded.
In thermally-assisted magnetic recording, a method using near field light is known as a method to heat to the magnetic recording medium. The near field light is a type of electromagnetic field that is generated around a substance. Ordinary light cannot be focused to a region that is smaller than its wavelength due to diffraction limitations. However, when light having an identical wavelength (coordinated wavelength) is irradiated on to a microstructure, near field light depending on the scale of the microstructure is generated, it enabling the light to be focused on to a minimal region, such as a region only tens of nm in size. As a practical method to generate the near field light, a method using a plasmon antenna is generally known. The plasmon antenna is a metal that is referred to as a near field light probe that generates near field light from plasmon excited by light.
Direct irradiation of light generates the near field light in the plasmon antenna. However, with this method, a conversion efficiency to convert irradiated light into near field light is low. Most of the energy of the light that is irradiated on the plasmon antenna is reflected by the surface of the plasmon antenna or is converted into thermal energy. The size of the plasmon antenna is set to be no more than the wavelength of the light. Accordingly, the volume of the plasmon antenna is small. Therefore, the temperature of the plasmon antenna significantly increases according to the above-described generation of heat.
Because of the temperature increase, the volume of the plasmon antenna expands, and the plasmon antenna protrudes from an air bearing surface (ABS) that is a surface opposite to the magnetic recording medium. Accordingly, the distance of an edge part of the MR element positioned on the ABS from the magnetic recording medium increases, causing a problem. The problem is that servo signals recorded in the magnetic recording medium are barely sensed during the recording process.
Currently, a technology that does not directly irradiate light to the plasmon antenna is proposed. For example, the specification of U.S. Pat. No. 7,330,404 discloses such a technology. The technology is that light propagating through a waveguide such as an optical fiber is coupled in a surface plasmon polariton mode through a buffer portion to a plasmon generator so that the surface plasmon is excited on the surface of the plasmon generator. The plasmon generator has a near field light generator that is positioned on the ABS and that generates the near field light. At the interface between the waveguide and the buffer portion, the light propagating through the waveguide is totally reflected. However, at the same time, light penetration to the buffer portion is generated, which is referred to as evanescent light. When the evanescent light and collective oscillation of electric charges in the plasmon generator are coupled, the surface plasmon is excited in the plasmon generator. The excited surface plasmon propagates to the near field light generator along the plasmon generator, and generates the near field light at the near field light generator. According to this technology, the light propagating through the waveguide is not directly irradiated to the plasmon generator so that the excessive temperature increase of the plasmon generator can be prevented.
In an element, such as the magnetic recording element, formed by a thin film process, the waveguide is formed as a long and narrow member having a rectangular cross section. The waveguide is a core of the rectangular cross section, and the waveguide is covered by a clad. In some cases, the waveguide includes a member such as a spot-size converter to focus laser light. Moreover, the combination of the waveguide, the clad, the spot-size converter and the plasmon generator is referred to as a near field light generation element (or near field light generator).
The ABS is formed on the thin film magnetic head by a lapping process. During the lapping process, the thin film magnetic head stores static electricity. When the stored static electricity is discharged, generation of heat occurs due to the discharging. Similarly, during the production of a head gimbal assembly and the cutting of a wafer into a row bar, the static electricity is stored in the vicinity of the ABS. Accordingly, a similar phenomenon may occur. The plasmon generator is, generally, made of Au, Ag, Cu, Al, Pd, Ru, Pt, Rh, Ir or an alloy that is primarily composed of these metals. These metals have a large surface tension. Therefore, the generation of heat caused by the discharge of the static electricity causes grain growth (agglomeration) of these metal materials. Due to the grain growth, it is difficult to maintain a shape of the plasmon generator that is formed during wafer formation on the order of a nano-meter level, which significantly affects the generating efficiency of the near field light.
In a plasmon generator using evanescent light penetrated from the waveguide, a certain distance (length that the waveguide and the plasmon generator are overlapped) is required for coupling the plasmon. As a result, the volume of the plasmon generator tends to be larger than a volume of the plasmon antenna type plasmon generator. In other words, the plasmon generator using evanescent light tends to more store static electricity than the conventional plasmon antenna.
The objective of the present invention is to provide a magnetic recording element that restrains storage of static electricity and that decreases the deformation of a shape of the plasmon generator due to the discharge of the static electricity. Also, the objective of the present invention is to provide a slider, a head gimbal assembly, a hard disc device, and the like that include the above-described magnetic recording element.